Gas turbine engines (“GTE's”) produce power by extracting energy from a flow of hot gas produced by combustion of fuel in a stream of compressed air. In general, GTE's have an upstream air compressor coupled to a downstream turbine with a combustion chamber (“combustor”) in between. Energy is released when a mixture of compressed air and fuel is ignited in the combustor. The resulting hot gases are directed over the turbine's blades, spinning the turbine, thereby, producing mechanical power. In typical GTE's, one or more fuel injectors direct some type of fossil fuel into the combustor for combustion. Combustion of fossil fuel results in the production of some undesirable constituents in exhaust emissions. These undesirable constituents include nitrogen oxide (NO) and nitrogen dioxide (NO2), which are collectively referred to as NOx. In some countries, government regulations restrict the allowable level of NOx that may emitted by GTE's.
The amount of NOx emissions from a GTE increases with the flame temperature in the combustor. Therefore, one technique used by GTE manufacturers to meet NOx regulations is to reduce the flame temperature in the combustor of the GTE. Low flame temperature in the combustor may be achieved by reducing the fuel content in the fuel-air mixture fed to the combustor and by thoroughly mixing the fuel in the air before the fuel-air mixture is directed to the combustor. Such a well mixed fuel-air mixture with lower fuel content is referred to as a lean premixed mixture. While this lean premixed mixture reduces NOx emissions, reducing the fuel content in the mixture below a threshold value may cause the resulting flame to be unstable. The unstable flame may cause undesirable pressure oscillations within the combustor, eventually leading to smothering of the flame (called “lean blow-out”).
To provide a stable flame while meeting NOx emission regulations, some GTE fuel injectors provide for multiple fuel paths or fuel streams, such as a main fuel stream and a pilot fuel stream. In such a system, the main fuel stream provides lean premixed fuel to the combustor for low NOx operation, while the pilot fuel stream provides a source of rich fuel for flame stabilization and startup. The fuel delivered through these fuel streams may be liquid or gaseous. Some fuel injectors may also have the capability to deliver both liquid and gaseous fuel to the GTE. Due to the proximity of the fuel injector to the combustor, liquid fuel tubes providing liquid fuel to the pilot assembly (called pilot liquid tube) of the fuel injector may experience high temperatures during GTE operation. In addition to potential thermal damage to fuel injector components due to high temperature, prolonged exposure to these high temperatures may cause the pilot liquid tube to clog over time due to fuel coking. Damage caused to the pilot liquid tube may sometimes necessitate removal and cleaning of the tube in the field.
U.S. Pat. No. 5,404,711 ('711 patent), a patent issued to the assignee of the current disclosure, on Apr. 11, 1995, describes a GTE fuel injector with main and pilot fuel streams. While the injector of the '711 patent has proven to be reliable and robust, and has achieved wide commercial success, the pilot components of the '711 patent are permanently attached to the rest of the injector structure to provide a good seal against fuel and air leakage. Since the pilot assembly of the '711 patent likely experiences high temperatures due to its proximity to the combustion flame, liquid fuel lines may be susceptible to clogging due to coking. While the permanent attachment of the pilot components of the '711 patent prevents fuel and air leakage, removal and cleaning of liquid fuel lines in a field environment becomes difficult. The present disclosure is directed to solving one or more of the problems set forth above.